The basic function of the instrumental is to indicate the means by which an action is carried out. This is what the instrumental alone signifies, usually corresponding to the English prepositions with or by. However, the instrumental is also associated with the sense of accompaniment in many languages and Russian is one of them. To indicate the person or things that accompanies someone in Russian, a preposition is required: c+Ins 'with'. We will see how it works below. Finally, the instrumental has come to be associated with five specific place relations: 'behind', 'before', 'above', 'under' and 'between/among'. All of these meanings require prepositions, too. Here are the instrumental prepositions.

С(о)+Ins. It is important to understand that the English preposition with has two distinct meanings which are expressed in two different ways in Russian. with may indicate the means or instrument by which an action is carried out: He made the table with his hands/by hand. Notice that this meaning is also borne by the preposition by in some contexts. The other meaning is accompaniment; the object of with in this sense merely accompanies the noun modified by the prepositional phrase: He made the table with Sue or Sue arrived with her toolbox. This is a crucial distinction in Russian for the instrumental alone (without a preposition) expresses the former sense and the preposition с(о)+Ins marks only the second, sociative meaning.

The preposition с(о)+Ins is also used in a related sense to indicate the manner in which something is done when manner may be expressed by a noun, e.g. Он ел рыбу с некоторой неохотой "He ate the fish with a notable unwillingness". Both of these senses of с(о)+Ins are antonyms of без+Gen "without".

Володя пришел с друзьями.

Volodya came with his friends.

Алла пришла с цветами.

Alla arrived with flowers.

Он ходит только с трудом.

He can walk only with difficulty.

Она одевается со вкусом.

She dresses with taste.

Между+Ins. This preposition means either "between" or "among"  Russian does not distinguish between two objects and more than two objects in this sense as the English prepositions do (although, don't forget среди+Gen "among"). As usual, Russian dispenses with the little quirks that makes learning English so difficult.

Этосекрет между нами.

That's a secret between us.

Между нимиполное согласие.

There is complete agreement between them.

Над+Ins. To express the relation "over" or "above" the Russians use над+Ins regardless of whether the verb is a verb of motion or not.

Её картина висит над камином.

Her picture hangs over the fireplace.

Тучи стояли над городом.

Storm clouds hung over the city.

Он повесил винтовку над камином.

He hung his rifle over the fireplace.

Птица летела над домом.

A bird flew over the house.

Перед+Ins. To express the relation spatial "before" or "in front of" the Russians use перед+Ins, also regardless of whether the verb is a verb of motion or not. But перед+Ins is also used to indicate responsibility for something, where English uses to.

To express the relation spatial "under" or "beneath" the Russians use под+Ins if no motion is involved. The same preposition requires the accusative case if it accompanies a verb of motion.

Собаки лежат под крыльцом.

The dogs are lying under the porch.

Ребята пошли под дождём в кино.

The kids went to the movies in the rain.

Под+Ins can also mean "near" in the physical sense. (Под+Acc has the same meaning in reference to time.)

Серёжа живёт под Москвой.

Seryozha lives near Moscow.

У нее дача под Воронежем.

She has a dacha near Voronezh.

За+Ins. This is another multifunctional preposition. Its basic meaning is "behind" and "beyond", but is a busy little fellow that does a lot more than that.

To express the relation of being spatially "behind" or "beyond" something, Russian employs за+Ins if no motion is involved. The same preposition requires the accusative case if it accompanies a verb of motion.

Паша стоит за мной.

Pasha is standing behind me.

Его поля за лесом.

His fields are beyond the woods.

Даря живёт за городом.

Darya lives outside town.

За+Ins is also used to express "for" in two senses, explained elsewhere.